Bisprasin, a novel Ca(2+) releaser with caffeine-like properties from a marine sponge, Dysidea spp., acts on Ca(2+)-induced Ca(2+) release channels of skeletal muscle sarcoplasmic reticulum.

Bisprasin, a unique bromotyrosine derivative containing a disulfide linkage, was isolated from a marine sponge of Dysidea spp. This compound caused a concentration-dependent (from 10 to 30 microM) increase in the (45)Ca(2+) release from the heavy fraction of skeletal muscle sarcoplasmic reticulum (HSR) of rabbit skeletal muscle in the same way as does caffeine. The 50% effective concentrations of bisprasin and caffeine were approximately 18 microM and 1.2 mM, respectively, indicating that the (45)Ca(2+)-releasing activity of bisprasin was approximately 70 times more potent than that of caffeine in HSR. The bell-shaped profile of Ca(2+) dependence for bisprasin was almost the same as that for caffeine. Typical blockers of Ca(2+)-induced Ca(2+) release channels, such as Mg(2+), procaine, and ruthenium red, inhibited markedly bisprasin- and caffeine-induced (45)Ca(2+) release from HSR. This compound, like caffeine, significantly enhanced [(3)H]ryanodine binding to HSR. Scatchard analysis of [(3)H]ryanodine binding to HSR revealed that bisprasin and caffeine decreased the K(D) value without affecting the B(max) value, suggesting that both the drugs facilitate the opening of ryanodine receptor channels. The bisprasin- and caffeine-induced increases in [(3)H]ryanodine binding were further enhanced by adenosine-5'-(beta, gamma-methylene)triphosphate. These results suggest that the pharmacological properties of bisprasin are almost similar to those of caffeine, except for its 70-fold higher potency. Here, we present the first report on the pharmacological properties of bisprasin, which, like caffeine, induces Ca(2+) release from skeletal muscle SR mediated through the ryanodine receptor.